The invention relates to an application device for the simultaneous and uniform application of a foamable reaction mixture on to a surface, a device for the production of sandwich composite elements and a process for the continuous or discontinuous production of sandwich composite elements, especially foam composite elements with rigid and flexible outer layers.
For a long time, there has been a need for devices for the continuous production of sandwich composite elements in which the production rate can be increased to speeds of more than 15 m/min, preferably up to 60 m/min.
Up to now, oscillating mixing heads have been used for the continuous production of sandwich composite elements. In the known processes, the mixing head performs an oscillating movement across the width of the bottom outer layer and applies the still liquid reaction mixture on to the bottom outer layer by means of a casting rake or fan or spoon nozzle, which is arranged at a right angle to the mixing head and parallel to the bottom outer layer.
The mixing head is fixed to a guide rail, the so-called portal, above the bottom outer layer and is accelerated with the aid of electric motors and slowed before the reversal points. The raw materials for foaming are fed into the mixing head through flexible tubing. In addition, in some cases hydraulic or pneumatic hoses lead into the mixing head. The raw materials for foaming are introduced into the mixing head through nozzles and are mixed.
The reaction mixture then flows into the casting rake and exits through the regularly spaced holes. A uniform distribution of the reaction mixture oblique to the direction of transport is achieved by the length of the casting rake and its holes, as well as by the oscillating movement of the mixing head.
After the application, the reaction mixture foams up and rises as far as the top outer layer. During the foaming process it bonds the two outer layers before the foam solidifies and cures.
This production process is physically limited in terms of the production rate. Even if sufficiently strong motors, guide rails, hoses, mixing heads and casting rakes or fan or spoon nozzles were used, the reaction mixture would be taken out beyond the sides of the outer layers as a result of excessively high centrifugal forces at the reversal points. According to the prior art, production rates of more than 15 m/min cannot be achieved in the continuous production of sandwich composite elements using this application technique.
The technique of bringing the production rate to 60 m/min using stationary mixing head technology and rigid discharge systems is sufficiently well known. This process known as US technology (high-speed machines) consists substantially of three identical metering lines with separate feed and separate mixing heads and discharge systems. However, this technology does not have a distributor head such as that employed in the present invention. The known process is disadvantageous in that the reaction mixture leaving each of the individual mixing heads is also subject to different physical conditions in terms of pressure and temperature, which becomes apparent in the foam produced as reductions in product quality, such as uneven surface, smaller cell, and different thermal conductivity values due to reaction kinetics that differ from point to point.